A Change in the Radius of Rotation of F1-ATPase Indicates a Tilting Motion of the Central Shaft

F-1-ATPase is a water-soluble portion of FoF1-ATP synthase and rotary molecular motor that exhibits reversibility in chemical reactions. The rotational motion of the shaft subunit gamma has been carefully scrutinized in previous studies, but a tilting motion of the shaft has never been explicitly postulated. Here we found a change in the radius of rotation of the probe attached to the shaft subunit gamma between two different intermediate states in ATP hydrolysis: one waiting for ATP binding, and the other waiting for ATP hydrolysis and/or subsequent product release. Analysis of this radial difference indicates a similar to 4 degrees outward tilting of the gamma-subunit induced by ATP binding. The tilt angle is a new parameter, to our knowledge, representing the motion of the gamma-subunit and provides a new constraint condition of the ATP-waiting conformation of F-1-ATPase, which has not been determined as an atomic structure from x-ray crystallography.